The present invention relates to railway train brake apparatus and, in particular, to brake apparatus for releasing an automatic brake application at the locomotive independently of the cars of the train.
In present practice, the locomotive air brake system employs a control valve device capable of being selectively conditioned for either direct release type operation, as required when the locomotive is used in a freight train, or a graduated release type operation, as required when the locomotive is being employed in a passenger train. In addition, this control valve is provided with a quick release valve to release the control valve initiated automatic brake application on the locomotive independently of the car brakes. The quick release valve is actuated by depressing the locomotive independent brake valve handle. Since the locomotive automatic and straight air brake systems are connected to the brake cylinder relay valve through a double check valve, the automatic air brake is only released to a value corresponding to the position of the independent brake valve handle in the zone of application. A description of the foregoing locomotive air brake system devices and the system operation may be found in WABCO instruction pamphlet G-g-5071-6 entitled "26 Type Brake Equipment for Locomotive". This locomotive brake equipment is conventional and well-known to those in the railroad industry.
It has been proposed to substitute for the conventional locomotive control valve a freight car control valve, such as the conventional AB/D type control valve, when the locomotive is to be used strictly in a freight train. Since the AB/D type control valve is considerably less complex than the 26 type control valve traditionally employed on locomotives, a considerable cost savings can be realized. However, the conventional AB/D type control valve has no means for providing the independent release of the locomotive automatic air brake. Moreover, the conventional AB/D type control valve operates on the pressure equalization principle which differs from the proportioning principle on which operation of the 26 type control valve is based, thus precluding use of the conventional quick release valve with the AB/D type control valve.